Regenerator construction of a cold-gas refrigerator



1957 w. F. SCHALKWIJK ET AL 2,775,876

REGENERATOR CONSTRUCTION OF A COLD-GAS REFRIGERATOR Filed Jan. 5, 1955 INVENTORS WILLEM FREDERIK SCHALKWIJK LEENDERT DE LAN GE ADRIMN OOPMAN S AGE T REGENERATOR CONSTRUCTION OF A COLD-GAS REFRIGERATQR Willem Frederik Schalkwijk, Leendert de Lange, and

Adriaan Koopmans, Emmasiugel, Eindhoven, Netherlands, assignors to Hartford National Bankand Trust Company, Hartford, Conn., as trustee Application January 5, 1955, Serial No. 479,922. Claims priority, application Netherlands January 15, 1954 3 Claims.

The invention relates to a refrigerator comprising a space having a lower temperature and a space having a higher temperature, which spaces are in open communication with one another through a freezer having a temperature lower than 40 C., preferably lower than -60 C. in normal operation of the apparatus, through a regenerator made from wire material and through a cooler while the volume of these spaces are varied by one or more piston shaped "bodies. A gas in the aforesaid apparatus, being always in the same state of aggregation, performs a closed thermodynamic cycle. Such a refrigerator is called a refrigerator operating on the reversed hot-gas engine principle and often it is termed a cold-gas refrigerator. It is known that these refrigerators may be constructed in various ways, for example as displacerpiston machines, double-acting machines, machines in which the cylinders are at an angle to one another of machines in which the working space is combined with that of a hot-gas piston engine. v

The gas performing a closed thermodynamic cycle in the refrigerator may be chosen with respect to the requirements for the cold-gas refrigerator. If the refrigerator is intended to yield a cold production at 140 C. or higher, air will often be preferred. However, if the refrigerator is intended to yield a cold. production at very low temperatures, for example at 200 C., it will no longer be possible to use air (or nitrogen or oxygen). In this case other gases, for example hydrogen or helium are used.

According to the present invention the cold production of a cold-gas refrigerator has been measured to yield a cold production at a particular temperature and it has been found that with all these refrigerators the speed of of the gas in the regenerator must be chosen between definite limits. If the speed of the gas was chosen lower than the values indicated hereinafter, the flow losses of the gas in the regenerator were, indeed, low, but the specific power of the refrigerator was found to be reduced excessively.

If, however, the speed of the gas was chosen higher, the specific power was too low, since the flow losses had increased excessively.

The refrigerator according to the invention has the feature that in normal operation of the refrigerator the following formula applies to the mean speed of the gas in the regenerator:

v/ C1=C1N wherein N =ndn/ Ck and v=the mean speed of the gas in the empty regenerator space in cms. per second,

Ck=llh6 sound velocity in the gas at the temperature of the space having the higher temperature in crns./ sec. n=the number of revolutions of the crank shaft of the refrigerator per second, dh=the hydraulic diameter of the wire material of the regenerator in cms.,

2,775,876 Patented Jan. 1, 1957 ice 2 while C1 is at least 0.5 and at the most 1.5, preferably at least 0.75 and at the most 1.20.

The values indicated above may be expressed in coherent units.

The term hydraulic diameter of the wire material of the 1 regenerator is to be understood to mean herein the quotient of four times the surface of a sectional area of the wire at right angles to its direction of length and the circumference of this sectional area. Moreover, the term wire material is to be understood to mean both material having a substantially circular sectional area and ribbonshaped material. The regenerator of wire material may be constructed in various ways. For example, the wire material may be zig-zag and be coiled. As an alternative, the filler may have a non-uniform, curly structure or a felt-like structure. The term mean speed in the regenerator is to be understood to mean the quantity of gas passing through a plane in the center between the regenerator head surfaces, divided by the sectional area of the empty regenerator at that area. Since the temperature of the cooler with different machines will often be substantially equal, Ck may in many cases have the following values:

. ems/sec. Hydrogen 1.33.10 Helium 1,010.10 Air 0.345.10

all values measured at 25 C.

The invention will be described more fully with reference to one embodiment.

The figure shows a cold-gas refrigerator of the displacer piston type. This machine comprises a cylinder 1 in which a displacer piston 2 and a piston 3 move up and down with substantially constant phase difference. To this end the displacer piston is coupled through a connecting rod system 4 with a crank of a crank-shaft 5, whereas the piston is coupled by means of a connecting rod system 6 with cranks of the same crankshaft 5. The space 7 over the displacer piston 2 is the space having the lower temperature and this space communicates through a freezer 8, a regenerator 9 and a cooler 10 with a space 11, the spa-cc of higher temperature which is acted upon both by the displacer piston and by the piston. The refrigerator may be driven by an electric motor 12, or other suitable type of motor.

The working space of the refrigerator is constituted by the spaces 7 and 11 and the ducts in the freezer, regenerator and cooler with any connecting ducts. In this Working space a gas being always in the same state of aggregation performs a thermodynamic cycle, the gas expanding mainly in the space 7 and being mainly compressed in the space 11.

Owing to the thermodynamic cycle performed in the machine the freezer assumes a low temperature, so that by means of this freezer a medium located outside the machine may be cooled. This medium, for example air, may be supplied through an opening 16 to a condenser space 17, in which it condenses on vanes 18 of the freezer 8, the condensate being conducted away through a duct 19.

The regenerator coil 9 has a cold end surface 13 and a hot end surface 14. In the center between these end surfaces a plane 15 may be assumed; in this plane the mean velocity in the empty regenerator space, i. e. the space without the filler, must lie within particular limits. The formula V/Ck=C1N- wherein N=ndn/Ck applies to this mean velocity. The values must be expressed in coherent units, for example in cms. and seconds, or in inches and seconds.

If the gas in the refrigerator is hydrogen and if the temperature of the cooler is 25 C., Ck is 133x10 ems/sec. The speed of the machine is in this embodiment 25 rev./sec. The regenerator is made from wire material having a hydraulic diameter dn of 2 10 ems. N is 25X10 /1.33 l =3.76 so that N 2.32X10- The speed v must therefore, in accordance with the invention, exceed 0.5 1.33 1O 2.32 10" 154 ems/sec. and be not more than 1.5 1.33 10 2.32 10 :463 cms./sec. v is preferably at least 0.75 CkN- =231 ems/sec. and at the most 1.20 CkN- =372 ems/sec.

If the refrigerator is filled with air or helium, the corresponding values of Ck must be substitued in the formula.

While we have shown and described the preferred embodiment of our invention, it Will be understood that the latter may be embodied other than as herein specifically illustrated or described and that in the illustrated embodiment certain changes in the details of construction and in the arrangement of parts may be made without departing from the underlying idea or principle of the invention within the scope of the appended claims.

What is claimed is:

l. A refrigerator of the type described provided with a first space having a temperature of lower than 4() C. and a second space having a higher temperature than said first space further comprising a cooler, regenerator of wire material and freezer, said first and second spaces being in open communication with one another through said cooler, regenerator and freezer, cylinder means enclosing said first and second spaces, a gas of invariable chemical composition performing a closed thermodynamic cycle in said refrigerator, two pistons for reciprocation in said cylinder means to thereby vary the volume of said gas in said spaces, the mean speed of the gas in the regenerator being in accordance with the formula v/Ck=C1N- wherein N=ndh/Cic and v=the mean speed of the gas in the empty regenerator space in cms. per second, Clc=th sound speed in the gas at the temperature of the space having the higher temperature in cms. per second, n=the number of revolutions of the crankshaft of the refrigerator per second, and dh=the hydraulic diameter of the wire material of the regenerator in cms. where C1 is at least 0.5 and at most 1.5.

2. A refrigerator of the type described provided with a first space having a temperature of lower than -40 C. and a second space having a higher temperature than said first space further comprising a cooler, a regenerator of wire material and freezer, said first and second spaces being in open communication with one another through said cooler, regenerator and freezer, cylinder means enclosing said first and second spaces, a gas of invariable chemical composition performing a closed thermodynamic cycle in said refrigerator, at least one piston for reciprocation in said cylinder means to thereby vary the volume of said gas in said spaces, the mean speed of the gas in the regenerator being in accordance with the formula v/C1=C1N- wherein N ndn/Ck and v=the mean speed of the gas in the empty regenerator space in cms. per second, Ck=the sound speed in the gas at the temperature of the space having the higher temperature in cms. per second, n=the number of revolutions of the crankshaft of the refrigerator per second, and dh the hydraulic diameter of the wire material of the regenerator in ems. where C1 is at least 0.5 and at most 1.5.

3. A refrigerator of the type described comprising cylinder means, piston means adapted to reciprocate in said cylinder means and forming therewith a first space having a temperature lower than 40 C. and a second space having a higher temperature than said first space, and spaces being adapted to receive a gas of invariable chemical composition, a cooler, a regenerator of wire material, and a freezer, said spaces being in open communication with one another through said cooler, regenerator and freezer, a crankcase, a crankshaft in said crankcase operatively connected to said piston means, said piston means varying the volume of said gas in said spaces, the mean speed of the gas in the regenerator being in accordance with the formula v/Ck=C1N- wherein N=ndh/Clc and v=the mean speed in cms. per second, Ck=the sound speed in the gas at the temperature of the space having the higher temperature in ems. per second, N=the number of revolutions of the crankshaft of the refrigerator per second, and dh=the hydraulic diameter of the wire material of the regenerator in cms. where C1 is at least 0.5 and at most 1.5.

References Cited in the file of this patent UNITED STATES PATENTS 1,240,862 Lundgaard Sept. 25, 1917 2,397,734 Goebel Apr. 2, 1946 2,564,100 Du Pre Aug. 14, 1951 

